Fix tweepy.debug() by using six's module helpers.

tweepy/__init__.py

@@ -21,6 +21,5 @@ from tweepy.cursor import Cursor
 api = API()
 
 def debug(enable=True, level=1):
-    pass
-    # import http.client
-    # http.client.HTTPConnection.debuglevel = level
+    from six.moves.http_client import HTTPConnection
+    HTTPConnection.debuglevel = level